The model of fluid membrane shall be examined in detail with the disk membranes of rod outer segment of bovine retina. The focus is on the dynamic characterization of these membranes in order to extend the fluid mosaic model to account for long range, collective fluctuation modes. The possible causality or correlation between the dynamic variables describing the long range internal modes of these membranes and the photo-induced ion transport shall be sought. If the photo-induced Ca ion 2 gating is the primary excitation mechanism in the visual cycle and any correlation between the membrane dynamics and the effluxed Ca ion 2 is found, then a significant advance toward molecular delineation of the photoreceptor function will be made. Two principal techniques employed are the forward depolarized quasielastic light scattering and the acoustically induced depolarized elastic light. These probes for the membrane collective modes will be complemented by flameless atomic absorption for the quantitative determinations of the effluxed ions. The intact membranes isolated from bovine ROS that are osmotically swollen in suspending media shall be used exclusively.